Update README. (grpc#26572)

Updates the README file for performance tests.

tools/run_tests/performance/README.md

@@ -159,7 +159,11 @@ $ go tool pprof --text --alloc_space http://localhost:<pprof_port>/debug/heap
 
 The scripts in this section generate LoadTest configurations for the GKE-based
 gRPC OSS benchmarks framework. This framework is stored in a separate
-repository, [grpc/test-infra](https://github.com/grpc/test-infra).
+repository, [grpc/test-infra].
+
+These scripts, together with tools defined in [grpc/test-infra], are used in the
+continuous integration setup defined in [grpc_e2e_performance_gke.sh] and
+[grpc_e2e_performance_v2.sh].
 
 ### Generating scenarios
 
@@ -350,9 +354,8 @@ configurations will be created. The script produces a set of basic
 configurations, as well as a set of template configurations intended to be used
 with prebuilt images.
 
-The [examples](https://github.com/grpc/test-infra/tree/master/config/samples)
-in the repository [grpc/test-infra](https://github.com/grpc/test-infra) are
-generated by this script.
+The [examples](https://github.com/grpc/test-infra/tree/master/config/samples) in
+the repository [grpc/test-infra] are generated by this script.
 
 ### Generating configuration templates
 
@@ -364,8 +367,8 @@ configurations or templates.
 
 The example template in
 [loadtest_template_basic_template_all_languages.yaml](./templates/loadtest_template_basic_all_languages.yaml)
-was generated from the example configurations in
-[grpc/test-infra](https://github.com/grpc/test-infra) by the following command:
+was generated from the example configurations in [grpc/test-infra] by the
+following command:
 
 ```
 $ ./tools/run_tests/performance/loadtest_template.py \
@@ -431,15 +434,20 @@ different ways.
 
 Collections of tests generated by `loadtest_config.py` are intended to be run
 with a test runner. The code for the test runner is stored in a separate
-repository, [grpc/test-infra](https://github.com/grpc/test-infra).
+repository, [grpc/test-infra].
 
 The test runner applies the tests to the cluster, and monitors the tests for
 completion while they are running. The test runner can also be set up to run
 collections of tests in parallel on separate node pools, and to limit the number
 of tests running in parallel on each pool.
 
-The test runner is used in the continuous integration setup defined in
+For more information, see the
+[tools README](https://github.com/grpc/test-infra/blob/master/tools/README.md)
+in [grpc/test-infra].
+
+For usage examples, see the continuous integration setup defined in
 [grpc_e2e_performance_gke.sh] and [grpc_e2e_performance_v2.sh].
 
+[grpc/test-infra]: https://github.com/grpc/test-infra
 [grpc_e2e_performance_gke.sh]: ../../internal_ci/linux/grpc_e2e_performance_gke.sh
 [grpc_e2e_performance_v2.sh]: ../../internal_ci/linux/grpc_e2e_performance_v2.sh